A solid oxide fuel cell (SOFC) comprises an anode to which fuel (e.g. hydrogen gas) is delivered, a solid oxide electrolyte, and cathode to which oxygen (e.g. air) is delivered. An illustrative anode comprises a NiO-yttria stabilized zirconia (YSZ) mixture. An illustrative electrolyte comprises solid yttria stabilized zirconia (YSZ). An illustrative cathode comprises a lanthanum-strontium manganate mixture (LSM). A dense (nonporous) oxide electrolyte is necessary to provide a seal between the hydrogen fuel anode and oxygen in air at the cathode since leakage through the electrolyte reduces efficiency of the fuel cell.
The solid oxide electrolyte has been made as a thin film or layer by a number of processing methods including electron beam physical vapor deposition (EBPVD) such as described in U.S. Pat. No. 3,645,786 and British Patent 1 252 254. U.S. Pat. No. 3,645,786 describes deposition rates of only about 1 micron/minute and indicates that deposition rates of greater than 1.5 microns/minute yield electrolyte layers having mechanical stresses, which may cause breaking of the electrolyte layer.
British Patent 1 252 254 requires a gas atmosphere of a pressure of 10−1 to 10−2 mm of Hg during deposition of a solid electrolyte. For example, a helium gas atmosphere of 4×10−2 mm of Hg was used to deposit a glazed YSZ oxide layer on a nickel substrate at a deposition rate of about 1.5 microns/minute.
Other patents which describe EBPVD of solid oxide electrolyte as layers include U.S. Pat. Nos. 4,937,152; 5,932,368; 6,007,683; 6,673,130; 6,677,070; and published US application No US 2004/0096572 A1.
U.S. Pat. No. 5,741,406 describes radio-frequency sputtering of a dense YSZ electrolyte at a deposition rate of only about 4 microns/minute.
U.S. Pat. No. 5,716,720 describes an EB PVD method of depositing a columnar thermal barrier oxide coating layer on a substrate using a process gas (e.g. oxygen) introduced during deposition and coating parameters controlled to form a columnar coating microstructure that includes required intentional internal porosity to accommodate strain mismatch between a metallic substrate and the thermal barrier coating layer.